The present invention relates generally to a method for managing the thermal load on an internal combustion engine, and more particularly to a method for selectively altering the output horsepower of the internal combustion engine by adjusting the timing of a camshaft relative to the crankshaft.
Internal combustion engines are continuously subjected to thermal loads that are a product of the combustion process and its inherent inefficiencies. Excessive thermal loads can reduce engine efficiency and reliability, which may cause thermal damage to engine components. It may be necessary to use increased flow rate/capacity fuel injectors to lower the temperatures of the thermally affected engine components. Increased flow capacity fuel injectors, however, have the undesirable characteristic of exhibiting decreased fuel control at low load conditions, which may diminish catalytic converter efficiency and increase the amount of precious metals that are needed to manufacture the converter.
The thermal load on an internal combustion engine is directly proportional to the horsepower that is produced by the engine. The largest thermal loads typically occur while the engine is producing maximum horsepower. However, because there is a time delay between the onset of a high thermal load and its potentially damaging effects, an engine can typically withstand a potentially damaging thermal load for a period of time before experiencing a significant reduction in engine performance or damage to its components. Consequently, excessive thermal load is primarily a concern when an engine is operated at high horsepower for an extended period of time.
Since the thermal load on an engine is directly proportional to the horsepower that is generated, one method for reducing excessive thermal loads is to derate the engine, which limits the maximum horsepower that the engine can produce throughout its operating range. Although doing so would certainly reduce the thermal load on the engine, it will also unnecessarily limit the horsepower available at operating conditions that normally do not produce excessive thermal loads. Consequently, it would be desirable to selectively reduce an engine""s output only under those conditions in which an engine is likely to be subjected to an excessive thermal load.
Known methods for selectively reducing the thermal load on an engine consist of retarding spark advance and/or increasing an engine""s fuel/air mixture. Both of these methods, however, have limited effectiveness in reducing the horsepower produced by an engine and may not be capable of sufficiently reducing the thermal load on an engine at all operating conditions. Accordingly, there is a need for selectively reducing the horsepower output of an engine beyond that which can be achieved by merely adjusting spark advance and the fuel/air mixture.
The present invention is directed to a method for selectively adjusting the horsepower generated by an internal combustion engine to reduce the thermal load on the engine by adjusting the timing of a camshaft relative to a crankshaft. For a given engine operating condition, there is typically an optimum camshaft phase angle (i.e., timing) that will maximize engine performance. Operating the engine with its camshaft phase angle set to something other than its optimum degrades engine performance and reduces the horsepower output of the engine. The reduced horsepower produces a corresponding decrease in the thermal load on the engine.
In another feature of the invention, a camshaft phaser is used to adjust the timing of the camshaft. The camshaft phaser varies the phase angle of the camshaft relative to the phase angle of the crankshaft. An engine controller, utilizing a control algorithm, controls the operation of the camshaft phaser. The present invention incorporates additional functions in the control algorithm that modify the timing of the camshaft to control the thermal load on the engine.
The camshaft phaser is used to selectively adjust the timing of the exhaust camshaft relative to the timing of the crankshaft. Setting the exhaust camshaft phase angle to something other than its optimum degrades the volumetric efficiency of the engine and reduces the horsepower output of the engine. Moreover, the drop in horsepower produces a corresponding reduction in the thermal load on the engine.
In another feature, the camshaft phaser is used to selectively adjust the timing of an intake camshaft relative to the crankshaft. As is the case with the exhaust camshaft, de-optimizing the timing of the intake camshaft decreases engine performance and horsepower output, which in turn produces a corresponding reduction in the thermal load to the engine.
In yet another feature, two separate camshaft phasers, one attached to the exhaust camshaft, the other to the intake camshaft, simultaneously adjust the timing of both camshafts relative to the crankshaft. Adjusting both camshafts simultaneously allows for a greater reduction in the thermal load to the engine than is possible by only adjusting the timing of one or the other.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.